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Add a Compose healthcheck that requests Uptime Kuma’s internal listener at http://localhost:3001. The probe runs inside the container, so it should not use the host’s published address. A healthcheck reports whether the process is responding; it does not restart an unhealthy container by itself. Keep a separate restart policy such as unless-stopped when you want Docker to restart a process that exits.
Use this Docker Compose healthcheck
The following service follows Uptime Kuma’s documented Compose layout: the louislam/uptime-kuma:2 image, persistent data at /app/data, and port 3001 published for clients outside the container. The healthcheck uses curl -f and gives the application time to start before failures count.
services:
uptime-kuma:
image: louislam/uptime-kuma:2
ports:
- "3001:3001"
volumes:
- uptime-kuma-data:/app/data
restart: unless-stopped
healthcheck:
test: ["CMD", "curl", "-f", "http://localhost:3001"]
interval: 30s
timeout: 10s
retries: 5
start_period: 30s
volumes:
uptime-kuma-data:Place the healthcheck block at the same indentation level as image, ports, and volumes. If you already have an Uptime Kuma service, add only the healthcheck and retain your existing volume, network, and environment settings.
Why the probe uses localhost:3001
Compose executes test from inside the Uptime Kuma container. In the documented deployment, Kuma listens on port 3001 in that container, making http://localhost:3001 the direct path to the process being checked.
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The mapping "3001:3001" means “host port 3001 to container port 3001.” It lets a browser or another machine reach Kuma through the Docker host. It is not required for a healthcheck running in the container. Using the host’s LAN address, public DNS name, or a reverse-proxy URL would test a different path and could fail because of firewall rules, proxy configuration, or name resolution even when Kuma itself is healthy.
curl -f is significant: it exits with a failure status for HTTP error responses, so a server response such as 500 can make the container unhealthy. A normal successful HTTP response produces a successful probe. Verify that the exact Uptime Kuma image tag you deploy contains curl; healthchecks fail when the command is absent, even if the web application is working.
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What each healthcheck setting controls
Docker’s Compose file reference defines healthcheck.test as the command used to determine whether a service container is healthy. List syntax begins with CMD, CMD-SHELL, or NONE. The example uses CMD, which runs curl directly without a shell.
| Setting | Example | Effect |
|---|---|---|
test |
["CMD", "curl", "-f", "http://localhost:3001"] |
Runs the HTTP probe inside the container. The command must exist in the image. |
interval |
30s |
Waits 30 seconds between scheduled probes after the container has started. |
timeout |
10s |
Marks an individual probe failed if it does not finish within 10 seconds. |
retries |
5 |
Requires five consecutive failures before Docker reports unhealthy. |
start_period |
30s |
Provides startup grace time. Failures during this period do not count toward the retry limit unless a probe succeeds first. |
These numbers are practical starting values, not performance measurements or universal defaults. One published Compose example uses the same 30-second interval, 10-second timeout, and five retries but allows a two-minute startup period. Another uses three retries, a 10-second startup period, and a five-second timeout. Choose values from the startup time you actually observe on your host: increase start_period for a slow disk or first-run initialization, and keep timeout long enough for normal response latency without hiding a genuinely stuck process.
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Compose versions that support it may also accept start_interval, which controls the interval during the startup period. It is optional; the four settings in the example work on broadly supported Compose implementations.
Apply the change and verify health
- Save the edited file as your Compose project’s YAML file, commonly
compose.yamlordocker-compose.yml. - From that directory, recreate or update the service:
docker compose up -d - Check the summary status:
docker compose psLook for a health indication such as
healthyafter the startup grace period. During initialization, the state may bestarting. - For the complete health record, first identify the container name with
docker compose ps, then run:docker inspect <container> --format '{{json .State.Health}}'This displays recent probe output, exit codes, timestamps, and the current status.
- If the service remains unhealthy, inspect application output:
docker compose logs uptime-kumaUse the service name from your file if it differs from
uptime-kuma.
The commands above are verification steps to run on your host. A health result is based on the command’s exit status, not on whether the container is merely running.
Health status is not automatic recovery
A healthcheck adds a state—starting, healthy, or unhealthy—to the container. It does not, by itself, restart a container that is responding incorrectly. The restart: unless-stopped line addresses a different event: Docker can restart the container when its main process exits, while still respecting an explicit stop by an administrator.
An application can therefore be unhealthy while its process continues running. If you need an orchestrator, watchdog, or external automation to react to that state, configure it separately and define what action is safe. Do not assume that adding healthcheck changes restart behavior.
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Make other Compose services wait for Kuma
Healthchecks become useful for startup ordering when another service must not be created until Uptime Kuma answers successfully. Docker Compose supports a long-form dependency with condition: service_healthy:
services:
uptime-kuma:
image: louislam/uptime-kuma:2
ports:
- "3001:3001"
volumes:
- uptime-kuma-data:/app/data
restart: unless-stopped
healthcheck:
test: ["CMD", "curl", "-f", "http://localhost:3001"]
interval: 30s
timeout: 10s
retries: 5
start_period: 30s
reporting-job:
image: your-reporting-image
depends_on:
uptime-kuma:
condition: service_healthy
volumes:
uptime-kuma-data:Compose waits for the dependency’s healthcheck to pass before creating the dependent service. This controls creation order; it does not guarantee that Kuma will remain healthy forever or that an already-created dependent process will be restarted when Kuma later becomes unhealthy.
Choosing between common probe commands
curl -f
This is the clearest option when the image includes curl. The -f flag turns HTTP error responses into a nonzero exit code, allowing Docker to distinguish an error response from a successful request.
curl -L
One published Uptime Kuma Compose example uses curl -L localhost:3001. The -L option follows redirects. This can be useful if the endpoint redirects during startup, but it does not provide the same explicit HTTP-error handling as -f unless you combine the flags, for example curl -fL http://localhost:3001. Use the form that matches the response behavior you want to treat as healthy.
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CMD-SHELL
Use CMD-SHELL only when you need shell operators, environment expansion, or a compound command. Shell syntax adds another failure point and should not be used merely because it is familiar. In every form, confirm that the selected client and its options are installed in the image.
External URL probes
An external route through a proxy or host address answers a different question: whether the entire network path works. It is not a substitute for the in-container check when your goal is to verify Kuma’s own listener. If you need both guarantees, keep the container healthcheck local and monitor the externally reachable URL as a separate monitor.
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Troubleshoot an unhealthy Uptime Kuma container
The healthcheck says the command is missing
An error such as “executable file not found” means the image does not contain curl at the expected path. Inspect the image’s available HTTP client and change test to a command that is actually installed, or select an image variant that includes the required client. Do not leave a known-missing command in the Compose file: it will report failure continuously.
The container is still starting when probes fail
Increase start_period to cover the slowest normal startup, including database initialization and filesystem latency. Keep interval, timeout, and retries aligned with the detection delay you can tolerate. A longer grace period prevents false alarms but also delays detection of a real startup failure.
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The probe returns an HTTP error
Run an interactive request from inside the container or review the health log shown by docker inspect. Confirm that Kuma is listening on port 3001, then inspect docker compose logs for application errors. A 4xx or 5xx response is expected to fail when -f is present; removing -f would hide those HTTP errors rather than fix them.
The app responds, but data operations fail
Uptime Kuma stores its data under /app/data. The project README warns that NFS filesystems are not supported for this data directory and recommends a local directory or Docker volume. A passing HTTP healthcheck cannot detect or repair database corruption, unsupported filesystem behavior, or intermittent storage. Treat storage reliability as a separate operational check and keep the data volume on supported local storage.
The host port is unavailable
A host-port conflict affects external access but is not normally the reason for an in-container probe to fail. Check the published port mapping and any other service already binding host port 3001. The healthcheck should continue to target localhost:3001 inside the Kuma container.
Quick Recap
Operational checklist
- Use
louislam/uptime-kuma:2or the image tag you have intentionally selected. - Persist
/app/dataon a supported local directory or Docker volume; avoid NFS for this path. - Target
http://localhost:3001from the container, not the host-published address. - Use
-fwhen HTTP error responses should make the probe fail. - Confirm the image contains the client command used by
test. - Set
start_periodfrom observed startup time rather than copying a value blindly. - Keep
restartpolicy separate from health status. - Run
docker compose up -d, then verify withdocker compose psanddocker inspect. - Use
depends_on: condition: service_healthyonly when a dependent service genuinely must wait for Kuma.
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